Arrangement and method for cooling of coolant in a cooling system in a vehicle

ABSTRACT

An arrangement and a method for cooling coolant in a cooling system in a vehicle: The cooling system includes a first cooling circuit, a first coolant pump ( 11 ) to circulate coolant through the first cooling circuit, a first radiator ( 13 ) to cool the coolant, and a thermostat ( 12 ) which opens to direct coolant to the first radiator ( 13 ) when the coolant is above the thermostat&#39;s regulating temperature (t 2 ); and a second cooling circuit includes a second radiator ( 20 ) to cool coolant. A flow device ( 23, 29 ) selectively transfers a portion of coolant from the first cooling circuit to the second cooling circuit, so that this portion of the coolant is cooled in the second radiator ( 20 ) when the coolant in the first cooling circuit is within a temperature range defined by a lowest temperature (t 1 ) at which the coolant initially needs cooling and a highest temperature which is equal to the thermostat&#39;s regulating temperature (t 2 ).

BACKGROUND TO THE INVENTION AND PRIOR ART

The present invention relates to an arrangement and a method for cooling of coolant in a cooling system in a vehicle according to the preambles of claims 1 and 11.

The coolant in a cooling system for cooling of a combustion engine in a vehicle needs to be at an operating temperature which is usually within the range 80-90° C. The cooling system usually comprises a thermostat which regulates the coolant's temperature in the cooling system. In operating situations where the thermostat finds that the coolant is below the desired operating temperature, it will be in a closed state whereby the coolant is led to the engine without cooling. Operating situations where the thermostat finds that the coolant is above the desired operating temperature will put the thermostat into an operating state in which it directs the coolant to a radiator for cooling before it is led back to the engine. The radiator is usually situated in the vehicle's front section where the coolant is cooled by air forced through the radiator by a radiator fan. The radiator which cools the coolant in the cooling system of heavy vehicles will have a large cooling capacity and therefore be quite expensive to procure.

Conventional thermostats switch abruptly between the closed state and the open state, subjecting the radiator and connecting units in the cooling system to very rapid temperature changes which cause large thermal stresses on the material of the radiator. The radiator and connecting units may at one moment be exposed to a temperature of the surroundings which in winter may be extremely low, but immediately thereafter be exposed to a temperature of around 100° C. when the thermostat opens and a large amount of warm coolant is circulated through the radiator and the connecting units. Problems occur in particular if the coolant's temperature begins to oscillate about the thermostat's regulating temperature, a situation which the radiator is very frequently subject to large thermal stresses very likely to shorten its service life. The service life of a radiator depends largely on how many times it is warmed and cooled.

SUMMARY OF THE INVENTION

The object of the present invention is to propose a cooling system in a vehicle which reduces the risk of a thermostat opening and closing frequently and the consequent risk of a radiator in the cooling system being frequently subject to large thermal stresses.

The above object is achieved with the cooling system defined in the characterising part of claim 1. The cooling system according to the invention thus comprises a second cooling circuit with a second radiator. When the coolant in the first cooling circuit reaches an initial temperature at which it initially needs to be cooled, a portion of it is led to the second cooling circuit, in which it is cooled in the second radiator. The thermostat is closed so that the portion of the coolant which is not led to the second cooling circuit undergoes no cooling. The second radiator may have a lower cooling capacity than the first radiator. When the coolant which has been cooled in the second radiator is led back to the first cooling circuit, it is mixed with uncooled coolant in the first cooling circuit. The coolant which has been cooled in the second radiator slows the coolant temperature rise in the first cooling circuit more than it cools the coolant to a temperature below the initial temperature at which it initially begins to be cooled. The coolant temperature in the first cooling circuit is thus prevented from oscillating about the initial temperature. The second radiator will therefore not be subject frequently to thermal stresses caused by warm coolant from the first cooling circuit being intermittently led to the second cooling circuit. In this operating state no coolant will thus be led to the first radiator, which will therefore not be subject to thermal stresses caused by rapid temperature changes.

The second radiator is thus used to regulate the coolant's temperature within a range from the initial temperature to the thermostat's regulating temperature. If the coolant is gradually warmed to a temperature corresponding to the thermostat's regulating temperature, the thermostat will open and the coolant in the first cooling circuit will be directed automatically to the first radiator. The thermostat has here a higher regulating temperature than a conventional cooling system. It is less likely to begin to open and close frequently at this rather high temperature. If it does, there is also the possibility of adjusting the coolant temperature in the first cooling circuit by means of the second radiator.

According a preferred embodiment of the present invention, said flow means comprise a valve means which in a first position directs coolant from the first cooling circuit to the second cooling circuit and in a second position prevents its passing from the first cooling circuit to the second cooling circuit. A valve means can easily and quickly be switched between the two positions. It may with advantage be a three-way valve. Said flow means with advantage comprise also a control unit adapted to putting the valve means into the first position when it receives information that the coolant in the first cooling circuit is at a temperature within said temperature range. The control unit may be a computer unit with suitable software for this purpose. The control unit is with advantage adapted to receiving information from a temperature sensor which monitors the coolant's temperature at a location in the first cooling circuit. The sensor may for example monitor the temperature of the coolant after it has cooled the engine in the first cooling circuit. Alternatively, or in combination, it may detect the temperature of the coolant before it is led to the engine.

According a preferred embodiment of the present invention, the second cooling circuit comprises a second coolant pump and the control unit is adapted to controlling its activation. This second coolant pump is with advantage in an inactive state when the control unit has put the valve means into the first position and coolant from the first cooling circuit is passing through the second radiator. The first coolant pump in the first cooling circuit may here effect the circulation both of the coolant in the first cooling circuit and the portion of the coolant which is circulated in the second cooling circuit. The control unit activates the second coolant pump when coolant is to circulate internally in the second cooling circuit. The second coolant pump is with advantage driven electrically, since the operation of such coolant pumps is easy to regulate.

According a preferred embodiment of the present invention, said flow means are adapted to preventing coolant from being transferred from the first cooling circuit to the second cooling circuit when the coolant in the first cooling circuit is below the lowest temperature within said range. In this situation the coolant will not have risen to an intended operating temperature and therefore needs no cooling. The coolant here circulates only in the first cooling circuit, and since the thermostat is closed no coolant is directed to the first radiator in order to be cooled. In this operating state the cooling system works in the same way as a conventional cooling system.

According to another preferred embodiment of the invention, said flow means have the possibility of transferring and not transferring coolant from the first cooling circuit to the second cooling circuit in various operating situations where the coolant in the first cooling circuit is above the thermostat's regulating temperature. In operating situations which require an extra-large cooling capacity, as when the engine is under heavy load or a retarder is activated, it is appropriate to use both the first radiator and the second radiator to cool the coolant in the first cooling circuit. At other times the second cooling circuit needs to be able to operate separately and cool components and/or media intended to be cooled by it.

According to another preferred embodiment of the invention, the second cooling circuit comprises a connecting line via which coolant can be led from the first cooling circuit to the second cooling circuit, and a connecting line via which coolant can be led back to the first cooling circuit from the second cooling circuit after it has again passed through the second radiator. In this case the coolant from the first cooling circuit may pass through a relatively limited part of the second cooling circuit which comprises at least the second radiator.

According to another preferred embodiment of the invention, the first radiator and the second radiator are air-cooled. They are with advantage situated in a front section of the vehicle. They may be situated in regions of the vehicle such that the second radiator in substantially all operating conditions is cooled by air at a lower temperature than the first radiator. The second radiator may be in contact with surrounding air in the vehicle's front section, while the first radiator is located behind the second radiator in the front section. A radiator fan may here force a common air flow through the two radiators. Other air-cooled cooling devices such as charge air coolers or EGR coolers may be situated in the vehicle's front section and be cooled by the common air flow.

The object indicated in the introduction is also achieved with the method according to the characterising part of claim 11.

BRIEF DESCRIPTION OF THE DRAWING

A preferred embodiment of the invention is described below by way of example with reference to the attached drawing, in which

FIG. 1 depicts a cooling system in a vehicle according to an embodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 depicts a vehicle 1 powered by combustion engine 2. The vehicle may be a heavy vehicle and the engine a diesel engine. The exhaust gases from the engine's cylinders are led to an exhaust line 4 via an exhaust manifold 3. The exhaust gases in the exhaust line 4, which will be at a positive pressure, are led to a turbine 5 of a turbo unit, thus providing the turbine with driving force which is transferred via a connection to a compressor 6. The compressor compresses the air led into an inlet line 8 via an air filter 7. A charge air cooler 9 is situated in the inlet line 8 in a region A in a front section of the vehicle. The purpose of the charge air cooler is to cool the compressed air before it is led to the engine. The compressed air is cooled in the charge air cooler by air forced through the charge air cooler by a radiator fan 10 and the draught caused by the vehicle's forward movement. The radiator fan is driven by the engine by means of a suitable connection.

The engine 2 is cooled by coolant which is circulated in a first cooling circuit of the cooling system by a coolant pump 11. The first cooling circuit is provided with a thermostat 12. The coolant in the first cooling circuit is cooled in a first radiator 13 fitted in a forward section of the vehicle in the region A. This first radiator is situated downstream of the charge air cooler 9 with respect to the direction of cooling air flow in the region A. The first cooling circuit comprises lines 14, 15, 16 which lead the coolant from the first radiator to the engine. The coolant pump 11 is situated in the line 16. The first cooling circuit comprises lines 17, 18 which lead the coolant from the engine to the first radiator 13. The line 17 comprises a retarder cooler 19 to cool hydraulic oil in a hydraulic retarder. When the coolant is below the thermostat's regulating temperature, the thermostat directs the coolant from the line 17 to the engine via the lines 15, 16, a situation in which the coolant is therefore not cooled in the first radiator 13. When the coolant is above the thermost's regulating temperature, the thermostat directs it to the first radiator for cooling. The first cooling circuit is substantially similar to a conventional system for cooling a combustion engine, but with a difference in that the thermostat has a higher regulating temperature than that in a conventional cooling system.

The cooling system comprises not only the first cooling circuit described above but also a second cooling circuit containing a second radiator 20 provided with a second coolant pump 28 to circulate coolant in the second cooling circuit. This second coolant pump is situated in a line 22 in the second cooling circuit. A valve means in the form of a three-way valve 23 is connected to the line 22. When this valve is put into a second position, it directs the coolant from the line 22 to a line 24 and a second radiator 20 in the second cooling circuit. The second cooling circuit comprises also a line 25 which leads cold coolant from the second radiator 20 to an AC condenser 26 and a gearbox cooler 27. The line 25 is connected to the line 22. When the second coolant pump 28 is activated and the three-way valve 23 is in the second position, coolant is circulated through the second radiator. The coolant's temperature in the second cooling circuit will in substantially all operating states be lower than that of the coolant in the first cooling circuit, since the coolant can here be cooled by air at the temperature of the surroundings. The refrigerant in the AC condenser 26 and the gearbox oil in the heat exchanger 27 can therefore be cooled to relatively low temperatures.

Coolant from the first cooling circuit may be transferred to the second cooling circuit via a first connecting line 21 a connected to the three-way valve 23. This first connecting line may thus lead coolant from the line 16 in the first cooling circuit to the three-way valve. When the three-way valve is in a first position, it directs coolant from the first line 21 a to the line 24 and the second radiator 20. After it has passed through the second radiator, the coolant is led via the line 25 to a second connecting line 21 b which leads it back to the line 15 in the first cooling circuit. The cooling system comprises a control unit 29 to control the three-way valve 23 and the activation of the second coolant pump 28. In this case the control unit 29 receives information from a temperature sensor 30 which monitors the coolant's temperature in the line 17 at a location which is downstream of the engine 2 and upstream of the retarder cooler 19.

During operation of the vehicle, the control unit 29 substantially continuously receives information from the temperature sensor 30 about the coolant temperature in the first cooling circuit. After start-up, the coolant will be below an initial temperature t₁ when its cooling needs to begin. This initial temperature t₁ may for example be 80° C. When the coolant is at a temperature below t₁, the control unit will put the three-way valve 23 into the second position whereby no coolant is transferred from the first cooling circuit to the second cooling circuit. The thermostat 12 has a regulating temperature t₂ which is higher than the initial temperature t₁. This regulating temperature may for example be 90° C. The thermostat is therefore closed when the coolant is below t₁. It will therefore direct no coolant to the first radiator 13, and the coolant will be led back to the first coolant pump 11 and the engine 2 without cooling. In this operating state when the coolant is below the initial temperature t₁, the first cooling circuit may work in a similar way to a conventional cooling system. In this operating state there is normally no need for any cooling of the coolant in the second cooling circuit and the control unit 29 will not normally activate the second coolant pump 28, but it is possible to activate the second coolant pump 28 and circulate the coolant in the second cooling circuit if so desired.

The coolant in the first cooling circuit is progressively warmed by the engine 2. When the control unit receives information from the temperature sensor 30 that the coolant has reached the initial temperature t₁, it puts the three-way valve 23 into the first position. It also ensures that the second coolant pump 28 is not in operation. Part of the coolant flow in the line 16 will thus pass through the first connecting line 21 a to the three-way valve 23, which directs the coolant to the line 24 and the second radiator 20 in the second cooling circuit. The coolant is cooled in the second radiator by air at the temperature of the surroundings before being led through the AC condenser 26 in which it cools the refrigerant in the AC installation, and the heat exchanger 27 in which it cools the gearbox oil. The coolant is then led via the second connecting line 21 b to the line 15 and thus back to the first cooling circuit. The cold coolant is here mixed with coolant from the thermostat 12, which will thus be at a temperature higher than the initial temperature t₁ but lower than the thermostat's regulating temperature t₂. The cold coolant which has been cooled in the second radiator 20 thus undergoes cooling by the coolant which comes from the thermostat. The magnitude of this cooling depends inter alia on how much of the coolant in the first cooling circuit is cooled in the second radiator.

The second radiator 20 is significantly smaller than the first radiator 13. Although it uses air at the temperature of the surroundings to cool the coolant in it, it has significantly less cooling capacity than the first radiator. The cooling effect upon the coolant when mixed with the cold coolant from the second radiator is therefore clearly less than if the whole coolant flow in the first cooling circuit passed through the first radiator. The increase in the coolant temperature t is halted but the cooling of the coolant is not sufficient to bring it back below the initial temperature t₁. The possibility of the coolant's temperature beginning to oscillate between below and above the initial temperature t₁ is thus prevented in most situations, which means that its temperature may often stay within the range between t₁ and t₂ for a relatively long period of operation of the vehicle. A continuous coolant flow is in this case led to the second radiator 20 and is therefore not subject to any large thermal stresses caused by rapid temperature changes. During such a period of operation, the first radiator 13 will also be at a substantially constant temperature when not receiving any coolant at all and will therefore likewise not be subject to any large thermal stresses caused by rapid temperature changes.

If surrounding air is not too cold, the coolant's temperature will rise in certain operating states of the engine 2 to above the regulating temperature t₂ of the thermostat. When this happens, the thermostat will open and the coolant in the first cooling circuit be directed to the first radiator 13 in order to be cooled before being used again to cool the engine. When the control unit 29 receives information that the coolant is above the thermostat's regulating temperature t₂, it will put the three-way valve 23 into the second position, thereby halting the coolant flow from the first cooling circuit to the second cooling circuit. At the same time, it will set the second coolant pump 28 running to start the circulation in the second cooling circuit. When the three-way valve is in the second position, the first cooling circuit and the second cooling circuit function as two separate circuits. In this case the engine is therefore cooled by the coolant in the first cooling circuit, and the media in the heat exchangers 26, 27 by the coolant in the second cooling circuit. In this operating state, the coolant in the second cooling circuit will be at a clearly lower temperature than that in the first cooling circuit. This means that the media in the heat exchangers 26, 27 can be cooled to close to the temperature of the surroundings. There is a risk that the coolant may reach temperatures which oscillate about the thermostat's regulating temperature t₂, but this risk is not so great at this raised regulating temperature t₂ of the thermostat 12.

The thermostat thus has a significantly higher regulating temperature t₂ than a conventional thermostat with a regulating temperature corresponding to the initial temperature t₁. The difference between t₁ and t₂ may be of the order of 10° C., which means that the regulating temperature t₂ is not reached as often as the initial temperature t₁. The present cooling system also affords the possibility of varying the cooling of the coolant in the first cooling circuit by switching the three-way valve, making it possible to alter the coolant's temperature and thereby prevent any possible temperature cycling about the regulating temperature t₂.

There are also other situations in which it may be appropriate to direct coolant from the first cooling circuit to the second cooling circuit, e.g. if the control unit 29 receives information that there is risk of ice forming in the charge air cooler 9. The control unit may receive such information from a temperature sensor which monitors the temperature of the charge air close to the charge air cooler. Putting the three-way valve into the first position will direct relatively coolant from the line 16 in the first line circuit to the second radiator 20. The air which flows through the second radiator will thus undergo a marked temperature rise. The air reaching the charge air cooler 9 downstream will thus be at a clearly higher temperature than 0° C., causing any ice formed within the charge air cooler to melt. When the control unit receives information that the temperature of the charge air has risen back to an acceptable level, it will put the three-way valve 23 into the second position. Another occasion for putting the three-way valve into the first position is operating situations in which the engine is under heavy load or the retarder is activated. Such situations require a high cooling capacity for the coolant in the first cooling circuit. In this case the coolant may be cooled both in the first radiator 13 and in the second radiator 20, reducing the risk of the cooling system being overloaded.

The cooling system indicated above thus has several advantages. The problem of the thermostat switching frequently and warm coolant being led at short intervals to a cold radiator can be substantially eliminated. The service life of the first radiator 13 may therefore be considerably lengthened with a cooling system according to the present invention. The possibility is afforded of increasing the coolant's temperature at low loads, reducing fuel consumption. Moreover, the first cooling circuit may where necessary provide increased cooling capacity through the possibility of also using both the first radiator and the second radiator to cool the coolant.

The invention is in no way restricted to the embodiments described but may be varied freely within the scopes of the claims. 

1. An arrangement for cooling of coolant in a cooling system in a vehicle, comprising: the cooling system comprising a first cooling circuit which comprises a first coolant pump configured and operable to circulate coolant through the first cooling circuit, a first radiator configured and operable to cool the coolant in the first cooling circuit, and a thermostat at the first cooling circuit configured to open and when open, to direct coolant to the first radiator when the coolant in the first cooling circuit is above a regulating temperature (t₂) of the thermostat; a second cooling circuit which comprises a second radiator for cooling of coolant, a flow device which comprises a valve, when the valve is in a first position, the valve is configured and operable to direct coolant from the first cooling circuit to the second cooling circuit, and when the valve is in a second position, the valve is configured and operable to prevent coolant from passing from the first cooling circuit to the second cooling circuit; and the flow device further comprises a temperature sensor which detects the coolant temperature at a location in the first cooling circuit, a control unit which receives information from the temperature sensor, wherein the control unit is configured to put the valve into the second position when the coolant in the first cooling circuit is at a temperature below the lowest temperature (t₁) at which the coolant initially needs cooling and is also below the thermostat's regulating temperature (t₂) and in the first position when the coolant in the first cooling circuit is within a temperature range defined by the lowest temperature (t₁) at which the coolant initially needs cooling and a highest temperature which is equal to the thermostat's regulating temperature (t₂).
 2. A cooling system according to claim 1, wherein the second cooling circuit comprises a second coolant pump configured and operable to circulate coolant through the second cooling circuit; and the control unit is configured and operable for controlling activation of the second coolant pump.
 3. A cooling system according to claim 2, further comprising said flow device is configured and operable to selectively either transfer or not transfer coolant from the first cooling circuit to the second cooling circuit in operating situations where the coolant in the first cooling circuit is at a temperature above the thermostat's regulating temperature (t₂).
 4. A cooling system according to claim 3, further comprising the second cooling circuit comprises a first connecting line configured and operable to lead at least a part of the coolant from the first cooling circuit to the second cooling circuit, and a second connecting line configured and operable to lead the coolant back to the first cooling circuit from the second cooling circuit after the coolant has again passed through the second radiator.
 5. A cooling system according to claim 1, wherein the first radiator and the second radiator are air-cooled.
 6. A cooling system according to claim 5, wherein the first radiator and the second radiator are situated in regions of the vehicle such that in substantially all of the operating conditions of the radiators, the second radiator is cooled by air which is at a lower temperature than the first radiator.
 7. A method for cooling of coolant in a cooling system in a vehicle, wherein the cooling system comprises: a first cooling circuit which comprises: a first coolant pump configured and operable to circulate coolant through the first cooling circuit, a first radiator configured and operable to cool the coolant in the first cooling circuit, and a thermostat at the first cooling circuit configured to open and when open, to direct coolant to the first radiator when the coolant in the first cooling circuit is above a regulating temperature (t₂) of the thermostat; a second cooling circuit which comprises a second radiator for cooling of coolant and a flow device which comprises a valve, when the valve is in a first position, the valve is configured and operable to direct coolant from the first cooling circuit to the second cooling circuit, and when the valve is in a second position, the valve is configured and operable to prevent coolant from passing from the first cooling circuit to the second cooling circuit; and the method comprising: detecting the coolant temperature at a location in the first cooling circuit, receiving detected temperature information putting the valve into the second position when the coolant in the first cooling circuit is at a temperature below the lowest temperature (t₁) at which the coolant initially needs cooling and which is below the thermostat's regulating temperature (t₂) and putting the valve into the first position when the coolant in the first cooling circuit is within a temperature range defined by a lowest temperature (t₁) at which the coolant initially needs cooling and a highest temperature which is equal to the thermostat's regulating temperature (t₂). 